This invention relates to a small electronic apparatus with an optical input device and, more particularly, to a small electronic apparatus such as a digital wristwatch with a calculation function for optically entering input data such as numerical values and characters.
In a conventional electronic wristwatch with a calculation function, push-button switches mounted on the side surface of a wristwatch case are used as an external input means. Along with a variety of applications of electronic wristwatches as data processing equipment, demand has arisen for simple entering of data such as English letters and kana characters.
In order to respond to the above demand, an external input means comprising a ten key pad or letter keys on the surface of the wristwatch case has been proposed. However, a large mounting space is required for such an external input means. In addition, the waterproof structure of the wristwatch is complicated. Therefore, the conventional external input means cannot be suitably incorporated in a small electronic watch such as a wristwatch.
In order to solve the above problem, a conventional electronic wristwatch is proposed wherein a plurality of transparent touch electrodes are formed on the front surface of a protection glass plate for covering a display device. When a user touches the touch electrode, a switch input is performed.
In the conventional external input means of this type, however, the transparent electrodes are formed on the protection glass plate, which are easily damaged, thereby disconnecting the transparent electrodes. Since a number of electrodes are exposed to the outer atmosphere, static electricity and noise tend to be mixed in an LSI (large scale integrated circuit) of the wristwatch, resulting in circuit damage and operation failure.